<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .box{
            width: 100px;
            height: 30px;
            margin: 100px auto;
            background: #f90;
            position: relative;
        }
        .box:after{
            content: '';
            display: block;
            width: 0px;
            height: 0px;
            border-top: 6px solid transparent;
            border-bottom: 6px solid transparent;
            border-left: 12px solid red;
            position: absolute;
            right: -12px;
            top: 9px;
        }
    </style>
</head>
<body>
    <div class="box"></div>
</body>
</html>